1. Field of the Invention
This invention relates to a process for broadening the width of a bundle of parallel filaments having a band form and thereby preparing a thinner layer therefrom, which process comprises pinching the bundle along a direction-turning bar or bars arranged obliquely to the approaching direction of the bundle to the straight bar(s) along the surfaces thereof and turning the advancing direction of the bundle to an optional direction according to the required broadened width for the bundle.
The bundle of parallel filaments having a band form referred to herein means an untwisted bundle of parallel filaments such as tow, rovings, strands or the like of organic or inorganic filaments, arranged in parallel in the form of a band having a flat long rectangle in the cross-section.
The bundle of parallel filaments having a band form will often be hereinafter abbreviated merely to "bundle".
2. Description of the Prior Art
As to fabrics used for reinforcing industrial materials, etc., it has generally been regarded as most important that the fabrics are cheap and have sufficient strengths and uniformity; if a thin layer of parallel filaments having a uniform thickness is available, a reinforced material having an optional tenacity can be manufactured at a low cost by laminating the material as wefts and/or warps, and conventional woven or non-woven fabrics using expensive yarns obtained via a number of steps such as spinning, twisting, etc. will be replaced by the above laminated fabrics.
A prior art has been proposed wherein the width of a tow of crimped filaments is broadened by an arculate guide, utilizing the property that its filaments are internally connected in order, embracing each other by their crimps in the lateral direction, and the product is used as waddings or non-woven fabrics. However, according to the technique of this kind, a thin layer of 50 g/m.sup.2 or less is difficult to prepare and it is entirely difficult to broaden the width of uncrimped tow, rovings, strands, etc. having no connection in the lateral direction.
If a bundle of parallel filaments having a band form is laid straightly on a flat surface, and a straight bar is placed on the bundle obliquely to the lengthwise direction so that the filaments under the bar may be pinched and one end of the bundle is pulled up so that all the filaments may be directed to the same direction as that of pulling-up, then the width of the pulled-up bundle is varied according to the direction of pulling-up and the maximum width is obtained when the direction of pulling-up is perpendicular to the bar. Making use of this principle, the width of the bundle can be broadened. However, according to conventional prior art, it has been difficult to continuously carry out the above steps during the running course of the bundle. Namely, such a bundle is generally led by rotating rolls. In this case, the layer is sent toward their rotating direction along with the rotation of the roll surfaces; hence it always tends to approach the rolls in a direction perpendicular to the axial lines of the rolls. Thus it is impossible for usual pinch rolls to hold such a bundle pinching it obliquely to its advancing direction. Further, British Pat. No. 1,078,732 discloses a process wherein a film or a band is obliquely pinched by a pair of nip rolls. These rolls are specifically designed in order to prevent the film or band from sliding along the nip towards that side of the nip at the time of turning the direction of the film or band by the nip. Each of the nip rolls has a core and has its surface divided along generatices into at least two segments, each segment extending substantially along the length of the surface and being mounted to reciprocate along the core and to rotate with the core. According to the process, however, the structure of the device is so complicated that it is difficult to carry out the practice. Thus the process is not practical. No process utilizing simple stationary bar(s) has been found till now for holding a running bundle of parallel filaments by pinching it obliquely to its advancing direction.